There are no bearings on an LA to rust. The piston is aluminum, brass, and nickel. The only part that's iron is the crankshaft, and maybe the connecting rod. The crankshaft is supported by bushings. As long as you don't run it lean and burn the oil, there's very little to go bad. Run the fuel out at the end of the day, and you shouldn't have any problem. My guess is you're mistaking combustion byproducts and breakin wear for rust. Put it back together and go fly.

Brad